The present invention is directed to a combination drilling member formed of an axially elongated drill, such as for drilling rock, with a cutting bit at the leading end of the drill. The drill has an axially extending shaft with helical drilled material removal grooves extending between its ends. An auxiliary element is secured to the shaft.
Combination drilling members for drilling equipment are driven rotationally and include a drill and an auxiliary element positioned on the drill and secured to it so that torque can be transferred from the drill shaft to the auxiliary element. For example, the auxiliary element may be a milling head or a countersinking head. When the combination drilling member is used, initially a borehole is cut by the drill and subsequently, in the same operation, towards the end of the drilling operation, a depression or recess area is milled in the surface of a receiving material or of a component to be connected to it. In such a known combination drilling member, the milling or counter-sinking head is fixed to the shaft of the drill so that it cannot be detached, for example, by welding or integral molding. It can be noted immediately, in such combination drilling member, that a separate combination drilling member having the desired diameter, must be utilized for each drilling diameter to be used. If deeper countersinking or a recess of larger diameter is desired, a separate combination drilling member must be used. Moreover, drilling combination members cannot be obtained in all combinations. If the drill or the auxiliary element is damaged, such as damage to the milling or countersinking head, the combination drilling member is not usable and must be replaced as a whole.
From the patent publication EP-B-O 86 462, a combination drilling member is known, permitting a drilled hole to be cut in a receiving material in one working operation and, at the same time, a countersunk hole can be provided in the surface of an insulating panel to be secured to the receiving material. This known combination drilling member is formed with a drill and a milling head connected by a bolt to the shaft of the drill. The connection of the milling head to the shaft is detachable. As a result, the drill can be used with milling heads of different sizes, or a milling head can be used with drills of different diameters. If the milling head or the drill is worn or damaged, it can be replaced. For the detachable connection between the drill and the milling head, the shaft of the drill, adjoining the helical drilled material removal groove, can be provided with a thread. A stop shoulder on the shaft serves to fix the milling head along the axial head of the shaft. The metal milling head is provided with a hole having an internal thread, matched to the thread on the drill shaft. The milling head is connected to the shaft by bolts. To change the axial position of the milling head, washers of appropriate thickness can be positioned between the milling head and the stop shoulder.
As compared to the combination drilling members where thee auxiliary element, such as a milling head is fixed to the shaft, this known combination drilling member has the advantage that the milling head or the drill is replaceable, since the bolted connection can be removed. The bolted connection, however, is not particularly durable. Particularly when used with axially directed impact-supported drilling equipment, the durability of the bolted connection is considerably less than the useful lifetime of the drill. Due to the action of the axial impacts, the thread on the shaft of the drill and/or in the hole of the milling head is damaged in the course of time. As a result, the milling head may no longer be detachable from the shaft or, when the bolted connection is removed, the threads are damaged to such an extent that the milling head and/or the drill can no longer be connected to one another or connected with other drills or milling heads. In this combination drilling member known from the state of the art, a specially constructed drill is required. A thread must be formed on the shaft of the drill adjoining the drilled material removal grooves. For axially fixing the milling head to the shaft, a stop shoulder is required at the end of the threaded section of the shaft. Such an arrangement complicates the manufacture of the drill and makes the combination drilling member more expensive.